Ultrastructural changes of the basement membrane zone in benign lesions of the vocal folds.

The basement membrane zone (BMZ) of the epithelium of the vocal folds was investigated electron microscopically in 10 patients suffering from various benign lesions and in 3 controls. Various defects were observed: a thickening by deposition of electron dense material, a loss of normal architecture, and a near absence of normal hemidesmosomes and anchoring fibers. Beside these previously reported phenomena, many vesicles carrying electron dense material were found near the plasma membrane. The vesicles were observed at various stages of fusion with the plasma membrane, on the other side of which their content was discharged. In the cytoplasm an increase of mitochondria was seen. The amount of condensed chromatin decreased while the nucleoli increased in comparison with the controls. These observations are suggestive of a hyperactivity of the basal cells of the epithelium in response to vibratory stress.